1. Field of the Invention
The present invention relates to a lining material for pipe lines, preferably, pipe lines buried in the ground, such as sewage pipes, which lining material is capable of forming a rigid inner pipe for repair and/or reinforcement, and to a process for providing the pipe line with such a rigid inner pipe for repair and/or reinforcement. More particularly, the present invention relates to a lining material for existing pipe lines buried in the ground, for the purpose of effecting repair and/or reinforcement, and to a process for providing pipe lines with a fiber-reinforced or a fabric-fiber-reinforced plastic lining. The process comprises slidably inserting into the pipe line a lining material including a sheet impregnated with a thermo-hardenable resin, which sheet is somewhat overlapped in both lateral end portions to form a tubular sheet, inflating the lining material by introducing a pressurized fluid thereinto and internally heating the lining material to form an integrally solidified, rigid inner pipe within the pipe line.
2. Description of the Prior Art
It is well known that pipe lines, irrespective of whether they are constructed on the ground or in the ground, can be lined with a fiber-reinforced plastic material for the purpose of reinforcement and/or repair. Pipe lines buried in the ground cannot easily be provided with a lining, or be inspected for any damage to the pipe line. Accordingly, special techniques and materials are needed for lining pipe lines buried in the ground, such as gas pipe lines, city water pipe lines and sewage pipe lines. In the past, various lining materials have been proposed for repair and/or reinforcement of such underground pipe lines. In recent years, a tubular mat of a strong fibrous material impregnated with a liquid thermo-hardenable resin, which is overlapped in both lateral end portions so as to be slidable and interposable between an inner tube and an outer film and is then heated to thicken the resin, has been proposed as a pipe-lining material. This mat itself is called "Sheet Molding Compound" (referred to hereinafter as SMC) by ASTM. This SMC lining material is manufactured, for example, by spreading a strong fibrous material such as glass fiber over a plastic film capable of easily splitting off, to form a fibrous mat, impregnating the fibrous mat on the film with a thermo-hardenable resin such as styrene or an unsaturated polyester, overlaying the mat with a tubular film and heating the mat under controlled conditions to thicken the resin by effecting partial polymerization of the resin. In this case, the resin-impregnated mat on the tubular film is overlapped at both of its lateral end portions so as to be slidable in both directions to form a tubular mat. The two films on both sides of the resin-impregnated mat serve to prevent evaporation of the thermo-hardenable resin in the mat but the outer film is split off prior to being inserted into pipe lines.
This lining material containing SMC as the main component affords, after curing, a rigid fiber-reinforced plastic (FRP) lining on the inner surface of pipe lines, thereby attaining the purpose of reinforcement and/or repair of the pipe lines. However, this lining material has the drawback that when it is inserted into pipe lines, especially long or curved ones, an extremely strong force is applied on the SMC due to frictional resistance against the inner surface of the pipe lines whereby the SMC is locally stretched and reduced in its thickness or suffers from various other damage, and in the extreme case, breaks down in the locations where the damage is serious. As the SMC lining material has a number of disadvantages to be overcome in addition to the above mentioned problems, a new type lining material was proposed in Japanese Patent Appln. No. Hei 2-95880 (referred to hereinafter as Ref. 1). Disclosed in Ref. 1 is the newest lining material now currently used which comprises, in place of the SMC mat, a sheet comprising a fabric and a mat of fibers of high tenacity impregnated with a thickened liquid thermo-hardenable resin to form a fabric-fiber-reinforced composite molding sheet (referred to hereinafter simply as FCM-sheet). The FCM-sheet is also coated on both sides with two plastic films, one of which constitutes an outermost layer capable of easily splitting off before insertion of the lining material into the pipe lines. The stretchability of SMC under strong tension, which is one of the major disadvantages of SMC, is overcome to a certain degree by the FCM-sheet since a fabric in addition to fibers is impregnated with the thermo-hardenable resin, unlike the SMC sheet wherein fibers alone are impregnated with the resin. The resultant FCM sheet is thus resistant to biaxial tension. However, both SMC and FCM-sheet lining materials are similar in appearance since they are made up by overlapping both lateral end portions of the sheet material with each other to form a tubular material in such a manner that the overlapped portions of the tubular material are somewhat slidable in circumferentially opposite directions in compliance with the diameter of the pipe lines. In order to facilitate insertion of the lining material into a pipe line, the diameter of the tubular sheet, the lateral end portions of which are overlapped with each other, is normally smaller than the inner diameter of the pipe line. However, the lining material once inserted into the pipe line is inflated to bring it into contact with the inner surface of the pipe line prior to curing.
Among underground pipe lines, a sewage pipe line is usually made of a porcelain pipe or a Hume concrete pipe and thus is brittle and easily broken by earthquake or any vicinal underground work accompanying vibration. Otherwise, sewage pipe lines, if superannuated, become so brittle that they often undergo local breakage or rupture or are damaged so as to the extent that they can fall into pieces. When such brittle sewage pipe lines are lined with either the SMC or the FCM-sheet lining material for reinforcement, the lining material in the form of a tube formed by overlapping both lateral end portions of the sheet so as to be slidable in circumferential direction is inserted into such pipe lines and the tubular lining material is then inflated internally by fluid pressure whereby the overlapped lateral end portions are slid in compliance with the inner diameter, i.e. along the inner circumferential length of the pipe lines. If the pipe lines have a locally broken portion, the lining material expands out of the broken portion by internal pressure whereby the overlapped lateral end portions of the lining material are excessively slid to form a cleavage. If the pipe lines are considerably superannuated as a whole, they will rupture over a significant portion of their length for the reason that they are pressed internally by the expanding lining material and thus will locally fall into pieces. In this case, sliding of the overlapped lateral end portions of the lining material goes too far so that the opening may be formed between the lateral end portions of the lining material over a significant length. Although the FCM-sheet can suppress stretchability caused by tension, as compared to the SMC sheet, this phenomenon commonly occurs irrespective of whether the lining material is SMC or FCM-sheet as both materials wherein the lateral end portions are weakly bonded merely by the thickened liquid resin are less resistant to internal expansion by fluid pressure.
This drawback in the case of using the SMC or FCM-sheet lining material can be exaggeratedly shown in the accompanying FIG. 1 wherein a lining material is inserted into a pipe line, especially a sewage pipe, having a broken portion and is inflated internally by fluid pressure. A pipe line 101 has a broken portion 102 enabling the lining material 103 made of SMC or a FCM-sheet to evaginate through the broken portion due to internal fluid pressure. For exaggeration's sake, the overlapped lateral end portions 104 of the lining material is just located in the broken portion of the pipe line so that the overlapped lateral end portions which weakly bonded by the aid of a thickened thermo-hardenable resin contained in the lining material are opened by the internally exerted fluid pressure. In this case, the inner tubular plastic film 105 also spreads out of the broken portion 102 of the pipe line, and finally ruptures due to internal fluid pressure causing a leak of the fluid therethrough. Even if the overlapped lateral portions 104 of the lining material are not located in the broken area 102 of the pipe line 101, the lining material 103 in the broken area 102 expands, permitting a separation of the lateral end portions of the lining material within the pipe line 101. Thus, the remaining tubular film 105 no longer functions as a reinforcing material for the pipe line 101.
Furthermore, it is noteworthy that the pipe line is sometimes surrounded by high pressure underground water. If the pipe line has a broken portion, a large amount of water will intrude into the pipe line through the broken portion whereby the pipe line becomes flooded or at least is submerged with water throughout. In this case, if a lining material is applied to the inner surface of such a pipe line, the lining material is externally wetted with water so that the lining material cannot be thermocured or at least needs a long period of time for curing, even if it is internally heated.
The FCM-sheet lining material disclosed in Ref. 1 is certainly superior in mechanical strength to the SMC lining material but the former is still unsatisfactory in mechanical properties for applying it to pipe lines. The SMC sheet in the FCM-sheet is poor in strength and elongation at the time of break-down whereas the fabric sheet in the FCM-sheet is great in strength and elongation at the time of break-down. Thus, the SMC sheet breaks down by a weaker force as compared with the fabric sheet. In case of the FCM-sheet usually employed as a lining material and comprised of a SMC sheet of 4.0 mm in thickness and a fabric sheet of 0.3 mm in thickness, for example, these sheets showed the following properties: a strength at break-down of 43 kg/5 cm and an elongation at the time of break-down of 1.8% for the SMC sheet, and a strength at the time of break-down of 273 kg/5 cm and an elongation at the time of break-down of 24% for the fabric sheet. When a tensile force is applied to the SMC sheet, the force is concentrated at a relatively weak portion so as to incur local elongation and break-down. On the other hand, the fabric sheet shows great elongation at the initial stage of the applied tensile force due to the stretching of the relaxed yarns in the fabric structure, but its resistance to tensile force is rapidly decreased after allowing the yarns to stretch to a certain degree. If the SMC sheet is integrally combined with the fabric sheet as in the FCM-sheet, the force locally exerted to the SMC sheet is dispersed so that the strength and elongation at the time of break-down are somewhat improved. However, in the case where the tensile force is increased beyond a certain limit, the SMC sheet alone in the FCM-sheet breaks down. In the above example, the strength of the SMC sheet at the time of break-down was 57 kg/5 cm and its elongation was 2.4%. Accordingly, if a strong tensile force beyond a certain limit is exerted at the time of inserting the FCM-sheet lining material into pipe lines, the SMC sheet layer alone will break, thus leading to a failure in the lining treatment. More specifically, the FCM-sheet lining material used for a conventional sewage pipe of 300 mm in diameter has a width of about 1000 mm and the strength of the SMC sheet layer thereof at the time of break-down is 1140 kg (57/50.times.1000). This apparently means that if a load of at least 1 ton is applied at the time of inserting the lining material into the pipe, there may be the possibility that the SMC sheet layer will break down. In general, the load at the time of inserting a lining material into a pipe line depends on the length of the pipe line. Thus, a significant load is applied to a lining material in the event the lining material is long and the pipe line is also long. If the length of a pipe line exceeds 80 meters, the maximum load applied to a lining material being inserted into the pipe line will sometimes exceed 1 ton. Further, when the pipe line is seriously damaged or is irregular in size or is curved, the load will readily exceed 1 ton even if the length of the pipe line is far less than 80 meters.
In general, a sewage pipe line is constructed by connecting a great number of Hume concrete pipes in series. If such Hume concrete pipes are broken locally, only the damaged portions are repaired by replacing the damaged pipe with a new Hume concrete pipe. It is very common in this case that the pipe where the broken portion is formed is cut in two positions so as to remove only the broken portion and the remaining pipe end portions are then interconnected with a repair pipe which has an outer diameter equal to the inner diameter of the cut pipes. If such a sewage pipe line has been repaired several times, the inner diameter of the pipe line varies according to the repaired positions. Accordingly, if the pipe line once repaired is again to be repaired, the second repair pipe becomes smaller in inner diameter than the first repair pipe. Thus, the pipe line becomes constricted by repair pipes having different diameters. If the pipe line is lined with a tubular lining material with a definite diameter, the lining material tends to form wrinkles in the locations of the multiple repairs where the diameter of the pipe line is considerably smaller.
The lining material introduced into a pipe line is applied evenly onto the inner surface thereof by conveying a pressurized fluid, e.g. compressed air to the inside of the confined lining material. The lining material in this state is then internally heated to cure the thermo-hardenable resin to form a rigid fiber and/or fabric reinforced plastic inner pipe as a whole. A general and simple method for heating the lining material internally is to confine it, for example, with mouthpieces provided with an inlet and outlet and to introduce superheated steam into the lining material in a confined state whereby the lining material is heated internally under pressure. The curing of the thermo-hardenable resin is effected within a short period of time at a high temperature. In the case of an unsaturated polyester, for example, curing of the resin proceeds rapidly by a self-exothermic reaction. However, the outer surface of the lining material is contacted with the pipe line and the pipe line is in turn contacted with the surrounding ground so that much heat supplied is lost. In order to heat the lining material sufficiently, therefore, the pressure of the superheated steam has to be elevated to about 3 kg/cm.sup.2 for heating the lining material at 100.degree. C. or higher. However, care should be taken, because Hume concrete pipes usually used for sewage pipes are poor in pressure-resistance and tend to rupture under a pressure of about 2 kg/cm.sup.2. This tendency is significant if the pipe line is superannuated. Therefore, in a conventional method for heating the lining material, high pressure steam cannot be used and a considerable period of time is needed for heating the lining material.
Under the above circumstances, a need arises for improving the means for applying a lining material to pipe lines having damaged portions, especially superannuated sewage pipe lines, in a simple and economical manner. Also, there is a great demand for developing a new type lining material which can be inserted into a pipe line having damaged portions with little difficulty and capable of forming a rigid fiber-reinforced or fabric-fiber-reinforced plastic (FRP) lining on the inner surface of such a pipe line.